Golf club heads come in many different forms and makes, such as wood- or metal-type, iron-type (including wedge-type club heads), utility or specialty-type, and putter-type. Each of these types has a prescribed function and make-up. The present invention will be discussed as relating to iron-type clubs, but the inventive teachings disclosed herein may be applied to other types of clubs.
Iron-type golf club heads generally include a front or striking face, a back, a toe, a heel, a top line, a hosel, and a sole. The front face interfaces with and strikes the golf ball. A plurality of grooves, sometimes referred to as score lines, is provided on the face to assist in imparting spin to the ball. The back can also be described as the back of the striking face and may vary in design, depending whether the iron-type golf club head is a blade, muscle back or cavity back design. The hosel is generally configured to have a particular look to the golfer, to provide a lodging for the golf shaft, and to provide structural rigidity for the club head. The sole of the golf club is particularly important to the golf shot because it contacts and interacts with the playing surface during the swing. The toe is the region of the golf club head that is distal to the shaft, while the heel is the region of the golf club head that is proximal to the shaft. The top line is the uppermost region of the golf club head, extending between the toe and heel of the golf club head.
In conventional sets of iron-type golf clubs, each club includes a shaft with a club head attached to one end of the shaft, and a grip attached to the other end of the shaft. The club head includes a face for striking a golf ball. The angle between the face and a vertical plane is called the loft angle.
The set generally includes irons that are designated number 3 through number 9, and a pitching wedge. One or more additional long irons, such as those designated number 1 or number 2, and wedges, such as a gap wedge, a sand wedge, and a lob wedge, may optionally be included with the set. Alternatively, the set may include irons that are designated number 4 through number 9, a pitching wedge, and a gap wedge. Long irons are typically designated with the numbers 1, 2, 3, 4 or 5. Mid-irons are typically designated with the numbers 6 or 7. Short irons are typically designated with the numbers 8 or 9. Wedges are typically designated with the letters P (pitching wedge), G (gap wedge), S (sand wedge), or L (lob wedge), or may be designated with the degree of the loft angle (e.g., 52°, 54°, 56°, 58°, 60°, etc.). Alternatively, the set may also include hybrid-type golf clubs, which typically replace the long irons, such as the 1, 2, 3, 4 and 5 irons. Each iron has a shaft length that usually decreases through the set as the loft for each club head increases from the long irons to the short irons. The overall weight of each club head increases through the set as the shaft length decreases from the long irons to the short irons. To properly ensure that each club has a similar feel or balance during a golf swing, a measurement known as swingweight is often used as a criterion to define the club head weight and the shaft length. Because each of the clubs within the set is typically designed to have the same swingweight value for each different lofted club head or given shaft length, the weight of the club head is often confined to a particular range.
The length of the shaft, along with the club head loft, moment of inertia, and center of gravity location, impart various performance characteristics to the ball's launch conditions upon impact and dictate the golf ball's launch angle, spin rate, flight trajectory, and the distance the ball will travel. Flight distance generally increases with a decrease in loft angle and an increase in club length. However, difficulty of use also increases with a decrease in loft angle and an increase in club length.
Iron-type golf clubs generally can be divided into three categories: blades and muscle backs, conventional cavity backs, and modern multi-material cavity backs. Blades are traditional clubs with a substantially uniform appearance from the sole to the top line, although there may be some tapering from sole to top line. Similarly, muscle backs are substantially uniform, but have extra material on the back thereof in the form of a rib that can be used to lower the club head center of gravity or improve feel. A club head with a lower center of gravity than the ball center of gravity facilitates getting the golf ball airborne. Because blade and muscle back designs have a small sweet spot, which is a term that refers to the area of the face that usually results in a desirable golf shot upon striking a golf ball, these designs are relatively difficult to wield and are typically only used by skilled golfers. However, these designs allow the skilled golfer to work the ball and shape the golf shot as desired.
Cavity backs move some of the club mass to the perimeter of the club by providing a hollow or cavity in the back of the club, opposite the striking face. The perimeter weighting created by the cavity increases the club's moment of inertia, which is a measurement of the club's resistance to torque, for example, the torque resulting from an off-center hit. This produces a more forgiving club with a larger sweet spot. Having a larger sweet spot increases the ease of use. The decrease in club head mass resulting from the cavity also allows the size of the club face to be increased, further enlarging the sweet spot. These clubs are easier to hit than blades and muscle backs, and are therefore more readily usable by less-skilled and beginner golfers.